qemu code read: change the file mode
kernel code test: kobject sysfs rely on the ktype

In function sysfs_open_file(), it will check the ktype of a kobject and get
its sysfs_ops.

In this example, I dump the ktype of a normal kobject and find the default
ktype is dynamic_kobj_ktype, which is assigned in kobject_create().
kernel code test: hlist init

This will test how hlist is implemented and used in kernel.
kernel code reading: net_dev_init()

Network namespace/network subsystem initialization.